Do not use JS to initialize the schedule

- Only use JS for the drag&drop functionality and to the set/alter the time and rooms of the EventSchedule object.

- Introduce has_many :events, through: :event_schedules association to get unscheduled event easily

app/controllers/admin/schedule_controller.rb

@@ -23,7 +23,7 @@ module Admin
       @schedule_id = params[:id].to_i
       schedule = Schedule.find(@schedule_id)
       @event_schedules = schedule.event_schedules
-      @unscheduled_events = @program.events - schedule.event_schedules
+      @unscheduled_events = @program.events - schedule.events
       @selected_schedule_id = @conference.program.selected_schedule.try(:id)
       @dates = @conference.start_date..@conference.end_date
       @rooms = (@venue && @venue.rooms.any?) ? @venue.rooms : [Room.new(name: 'No Rooms!', size: 0)]